I have a thread in "Rally Point" for a monthly THR shoot and have a bit to say on this subject.
You are asking for ideas for getting a better turn out for your "group shoots?" Well, you say you have several people who post saying they are interested, but then never show up. Either life got in the way, or they are wishy-washy about meeting up with you for whatever reason. Next time you have a group shoot, make sure someone has a digital camera and take a lot of pictures. You want to make it look like this was the coolest place to be. If you have access to cool or unusual firearms, bring them.
Now, there will always be people who will say "Bhahh! He's only bringing out an M-16 and a Galil. . . if it ain't belt-fed, it's not worth my time." But you'd be surprised at how may shooters have never fired an M-1 Garand or your grandfather's old 1903 Springfield.
Next, have something fun and unique to shoot at. Steel gongs are popular, as are watermelons, pumpkins, or whatever is in season and available at the local market. Or how about bowling pins painted up to look like your favorite third world dictator/leader of international terrorist ring?
Lots of people go to shoot at paper on their own, and others rarely make it out to the range. Give 'em a little extra incentive to crawl out of bed/pass up on that new movie/etc. Make them feel like they missed out if they didn't show up. Oh yeah, and post the pictures on your forum.
This may sound like a lot of work, and it is in the beginning. Once you get the ball rolling, however, it gets easier and easier. I was getting good turnout on mine with little work until bad weather got in the way recently.
Note to the guys who prefer to shoot alone:
Actually, I'm with you on that. I go to the range to shoot, not to talk (except, of course, when I am doing my own "group shoot"). On a normal day, I only talk to a few people at the range, and then, only during cease-fire. I like it when it's just me, my gun(s), my ammo, and my target. I crawl out of my comfort zone only once a month for my group shoots as a way of "sharing my sport."